The present invention refers to a construction of a brushless electric motor rotor and to a method for producing said rotor, carrying magnet elements which are internally circumferentially arranged and radially spaced from the lateral surface of the rotor.
In he construction of a brushless electric motor rotor, the permanent magnet elements are affixed to the core of said rotor to be concentrically mounted around the motor shaft. In this construction, the rotor is formed by longitudinally aligning a plurality of mutually overlapped metallic laminations defining a lamination stack, each metallic lamination having a plurality of circumferentially aligned windows which are angularly equidistant from each other and from the motor shaft, said windows being aligned to respective windows of the other metallic laminations of the lamination stack, in order to define axial housings into which the magnet elements are mounted and affixed.
In the prior art construction, each metallic lamination of the rotor lamination stack has a central portion provided with a central opening to be mounted to the motor shaft, and radially end portions, each defined externally to a respective window of the metallic lamination and incorporated to the central portion from the regions thereof located outside two consecutive windows.
In his prior art construction, the windows of each rotor lamination are defined so that the respective end edges are turned towards the peripheral edge of the respective rotor lamination, in a spaced position from said peripheral edge of the lamination, in order to define therein a structural annular region connecting two adjacent radially end portions to each other and to the central portion of the lamination through the spacing existing between the adjacent end edges of two consecutive windows.
The existence of a structural annular region permits the use of metallic laminations produced in a single piece and having windows which, posteriorly, with the formation o the rotor lamination stack, will define axial housings for the magnet elements.
While this known construction for a metallic lamination is adequate to be manufactured on a large scale, relatively easer to carry out, of low cost and which results in a highly reliable product, it has the deficiency of permitting losses of useful magnetic flow to occur, which fact is incompatible with the application to which the rotor is designed.
With this construction, only part of the total magnetic field of the rotor generated by the magnets interacts with the magnetic field of the stator, whereas the remaining of said total field is lost in the form of a dispersion field of both the rotor and the air gap. The rotor field losses occur due to the presence of steel with a structural function in the rotor lamination An the magnet end region. This region serves as a pathway to the flow lines of the dispersion field, which represent a non-used amount of the total field of the rotor.
Thus, it is an objective of the present invention to provide an electric motor rotor and a method for producing an electric motor rotor, which eliminates the magnetic flow losses due to the rotor dispersion field, has high energetic efficiency and high reliability, and which may be obtained with an easy, economical and industrially viable construction, without impairing the integrity and strength of the rotor.
These and other objectives are achieved by an electric motor rotor, comprising: a core, formed by a plurality of metallic laminations, which are axially and mutually overlapped and which are made from a magnetic material; polar peripheral portions in a magnetic material and affixed around the core; and an equal number of magnet elements, retained between the polar peripheral portions and the core, said rotor comprising a cylindrical lateral surface defined by the polar peripheral portions, which are circumferentially spaced from each other, and by intermediate peripheral portions provided between each two adjacent polar peripheral portions, said intermediate peripheral portions having throughout their longitudinal extensions reduced electrical conductibility and reduced magnetic permeability in relation to the core, at least in the regions connecting two adjacent polar peripheral portions, said rotor further comprising a pair of end caps for retaining the polar peripheral portions to the core. The present invention further comprises a method for producing an electric motor rotor of the type mentioned above, comprising the following steps: a providing each metallic lamination with a plurality; of windows, each window having end edges turned towards a peripheral edge of the respective metallic lamination, with the end edges of all the windows being contained in the same circumference; b- providing each metallic lamination, from its peripheral edge and at least in the regions radially aligned with the adjacent end edges of each two consecutive windows, with a respective radial extension, which is coplanar and external to said peripheral edge; c- overlapping the metallic laminations, defining over an end cap a lamination stack, so that each window of said laminations be axially aligned with respective windows of the other metallic laminations, defining, with the end cap, axial housings along the rotor; d- inserting an adhesive material into the axial housings; e- inserting into each axial housing a magnet element: f- mounting and affixing another end cap to the lamination stack, already retaining each magnet element to the respective axial housing: q- curing the adhesive material, retaining each magnet element to the respective axial housing; and h- removing each said radial extension, so that the peripheral edge of the metallic laminations defines the transversal contour of the finished rotor.